1. Field of the Invention
The invention relates to a mask assembly for use in the delivery of Non-invasive Positive Airway Pressure (NPPV) for therapy of Sleep Disordered Breathing (SDB).
2. Background Information
The application of Continuous Positive Airway Pressure (CPAP) for therapy of Obstructive Sleep Apnea (OSA) was first taught by Sullivan in U.S. Pat. No. 4,944,310 (Sullivan). In CPAP treatment for OSA, pressurized air or other breathable gas is provided to the entrance of a patient's airways at a pressure elevated above atmospheric pressure, typically in the range 4 to 20 cm H2O to “splint” open the patient's airways and prevent obstructive apneas. Apparatus to deliver NPPV therapy typically comprises a blower, an air delivery conduit and a patient interface. The blower may be programmed to deliver a range of different forms of therapy.
In one form, a constant pressure of air or breathable gas is provided to the patient. It is also known for the level of treatment pressure to vary from breath to breath in accordance with patient need, that form of CPAP being known as automatically adjusting nasal CPAP treatment as described in U.S. Pat. No. 5,245,995 (Sullivan and Lynch). In another form, a relatively higher pressure of gas may be provided in the patient mask during the inspiratory phase of respiration and a relatively lower pressure or atmospheric pressure being provided in the patient mask during the expiratory phase of respiration. In other modes, the pressure can be made to vary in a complex manner throughout the respiratory cycle. For example, the pressure at the mask during inspiration or expiration can be varied through the period of treatment. See, for example, U.S. Pat. No. 5,704,345 and International Publication Nos. WO98/12965 and WO99/61088, all of which are incorporated by reference herein. In this specification, the term NPPV therapy will be used to embrace all these forms of therapy.
The patient interface may take many forms, such as a nasal mask assembly, a nose and mouth mask assembly or nasal prongs assembly. A mask assembly typically, but not always, includes a rigid shell, a soft face-contacting cushion, a forehead support and headgear for securing the mask to the head.
In one known mask assembly, the headgear includes a cap portion with four straps. In use, the cap portion engages the occiput of the patient. Furthermore, in use, the two lower straps extend between the cap portion and a nasal mask while the two upper straps extend between the cap portion and a forehead support.
Some patient interfaces include quick release mechanisms. Since the patient must be able to sleep while wearing the patient interface, it must be comfortable. In addition, the patient interface must provide a good seal so any unintentional leak that occurs is minimized and any intentional leak is controlled. Since the shape of people's noses, faces and heads vary widely, from a commercial perspective, it is important to be able to manufacture patient interfaces which can accommodate this range of facial shapes without carrying excessive inventory. A number of patient interfaces have been designed with the goals in mind of patient comfort, ease of use, adjustability and the ability to accommodate a wide range of patient face and head shapes.
U.S. Pat. No. 5,243,971 (Sullivan and Bruderer) provides a nasal mask which is suitable for use in CPAP or NPPV therapy. The mask has a face-contacting portion mounted to a shell which is sized and shaped to overfit the nose region of an intended wearer, and the face contacting portion is in the form of a distendable membrane which is molded from an elastomeric material. The distendable membrane and the shell together define a chamber, and pressurized gas admitted to the chamber causes the membrane to distend outwardly from the shell. When placed in contact with the face of the wearer, the distendable membrane is caused to overlay the covered facial regions and, under the influence of the pressurized gas, to conform three-dimensionally with the contours of the overlayed regions. An orifice is formed within the membrane and is shaped and positioned to admit gas from the chamber to the nasal passages of the wearer. The contents of this patent are hereby incorporated by cross-reference.
U.S. Pat. No. 6,112,746 (Kwok and Styles) describes a nasal cushion which comprises a substantially triangularly shaped frame from which extends a membrane. The frame has a scalloped edge by which the cushion is affixed to a mask body. The membrane has an aperture into which the wearer's nose is received. The membrane is spaced away from the rim of the frame and its outer surface is of substantially the same shape as the rim. Respective notches receive the bridge of the wearer's nose. The wearer's nose is received through the aperture into the chamber within the mask body. The seal forming portion thus contacts both the surface of the wearer's nose and a portion of the wearer's face in the region between the base of the nose and the upper lip, and around the sides and over the bridge of the nose. The shape of the seal forming portion is particularly suited to effectively seal the difficult region of the facial contour that is the crease between the sides of the nose and the face. The contents of this patent are hereby incorporated by cross reference.
U.S. Pat. No. 6,119,693 (Kwok, Matchett and Grant) describes an adjustable forehead support for a nasal mask. An adjustable forehead support for a nasal or full-face mask is described wherein the forehead support may be adjusted for the different shapes and sizes of a facial profile. The forehead support utilizes a dual-arm system which adjusts the position of the forehead support vis-a-vis the mask and/or air flow tube. The angle of the mask to the face may be adjusted with the invention of the '693 patent. The contents of that patent are hereby incorporated by cross-reference.
In international patent application PCT/AU00/00097 (WO 00/78384), a forehead support is disclosed that is adapted to be secured to a respiratory mask. The forehead support includes a joining member for securing to the mask and a cushion frame pivotally mounted to the joining member. The cushion frame is adapted to locate one or more forehead cushions. The cushion frame is also adapted to pivot relative to the joining member. In one form the cushion frame is also selectively lockable at two or more predetermined angular positions relative to the joining member. A respiratory mask assembly comprising a respiratory mask and a forehead support adapted to be secured to the mask is also disclosed. The contents of this specification are hereby incorporated by cross-reference.
Pending U.S. application Ser. No. 09/482,718 (Lithgow), now U.S. Pat. No. 6,422,238 describes headgear for securing a respiratory mask to a patient that incorporates a quick release arrangement. The headgear has at least one strap extending from each side of the mask, the straps being releasably fastened rearwards of the patient's face to secure the mask. The headgear further includes release means in the form of a pull cord attached to an overlying strap at its region of fastening to the underlying strap and guided forward to be gripped at the front of patient. The contents of this specification are hereby incorporated by cross-reference.
A mask cushion for use with a mask assembly in NPPV therapy is disclosed in U.S. patent application Ser. No. 09/885,445, “Mask with Gusset” to Frater et al. filed on Jun. 21, 2001, now U.S. Pat. No. 6,986,352 and assigned to the assignee of the present application, which application is incorporated by reference herein. The mask system disclosed therein includes a suspension mechanism to allow relative movement between a face-contacting cushion and a mask shell. The suspension mechanism also provides a predetermined force to the cushion that is a function of mask pressure, displacement of the cushion or both. In one embodiment of that invention, the mask cushion assembly includes an inflatable gusset acting as the suspension mechanism.